Methods and configurations for catalyst regeneration

ABSTRACT

A catalyst regenerator ( 100 ) has a first section ( 110 ) and a second section (120) and is operated such that carbon from a carbon-contaminated catalyst ( 140 ) is converted to carbon monoxide in the first section ( 110 ) and that carbon monoxide is converted to carbon dioxide in the second section ( 120 ). The residence time of the oxygen-containing gas in the first and second sections ( 110, 120 ) is regulated in preferred configurations by the shape (e.g., diameter) of the first and second sections ( 110, 120 ).

FIELD OF THE INVENTION

The field of the invention is regeneration of spent catalysts, andparticularly spent catalysts containing carbon.

BACKGROUND OF THE INVENTION

Numerous known processes, and especially petrochemical processes such ascatalytic cracking, or hydrotreating employ solid phase catalysts tofacilitate the desired reaction. While most of the known catalystssignificantly improve these processes, prolonged operation andrelatively harsh process conditions frequently lead to deposition ofcarbon (typically in form of coke) on the catalyst, thereby at leastpartially inactivating the catalyst.

Consequently, numerous efforts have been made to regeneratecarbon-contaminated catalysts, which is often achieved by combustion ofthe carbon on the solid phase with oxygen to produce carbon monoxide andcarbon dioxide as a waste gas stream. Removal of carbon monoxide fromthe waste gas has become increasingly important due to increasinglystringent standards for atmospheric emission of waste gases, and thereare various methods and configurations known in the art to reduce carbonmonoxide emission from regenerator vessels.

For example, combustion of carbon to carbon dioxide may be performed inthe same regenerator vessel at relatively high temperatures (e.g., above1200° F.) to ensure combustion to carbon dioxide while substantiallyreducing the concentration of carbon monoxide in the effluent of theregenerator vessel (The combustion of carbon to carbon dioxide is atwo-step reaction via the intermediate carbon monoxide). Exemplaryconfigurations of such systems are described in U.S. Pat. Nos. 4,325,833and 4,313,848 to Scott, in U.S. Pat. No. 4,051,069 to Bunn, Jr., et al.,or in U.S. Pat. No. 4,991,521 to Green et al.

While relatively high temperatures generally reduce carbon monoxideemission, most, if not all regenerator vessels operating at such hightemperatures will typically require expensive metals and otherprotective structures to withstand the thermal stress. Moreover,depending on the particular nature of the catalyst, sintering may occurat such temperatures. Still further, due to the relatively slow overallrate of conversion, regenerator vessels operating at high temperaturestend to be relatively large.

To circumvent at least some of the problems associated with hightemperature, catalyst regeneration may be performed in separate vessels,wherein the carbon in the first vessel is incompletely combusted to amixture of carbon monoxide and carbon dioxide, and wherein the mixtureis then further combusted in a carbon monoxide boiler to carbon dioxide.Separate combustion of carbon monoxide in a carbon monoxide boiler tocarbon dioxide typically provides an effluent gas with relatively lowcarbon monoxide concentration (e.g., less than 500 ppm). However, carbonmonoxide boilers typically require significant quantities of energy forproper operation. Moreover, shutdown of the carbon monoxide boiler formaintenance or other reasons imposes a severe limitation on continuousoperation of catalyst regeneration, and typically reduces regenerationcapacity during shutdown at least 70%.

Thus, although many methods and configurations for catalyst regenerationare known in the art, all or almost all of them suffer from variousdisadvantages. Therefore, there is still a need to provide improvedconfigurations and methods for catalyst regeneration.

SUMMARY OF THE INVENTION

The present invention is directed to catalyst regeuneration in which acontaminant is in a two-step reaction removed from a catalyst andconverted to a product using an oxygen-containing gas, wherein the firststep in the two-step reaction is selectively performed in a firstportion of a vessel, and wherein the second step in the two-stepreaction is selectively performed in a second portion of a vessel,wherein control over the selective reactions is at least in partprovided by the residence time of the oxygen-containing gas in the firstand second sections.

Thus, in one aspect of the inventive subject matter, contemplatedregenerators have a first section fluidly coupled to a second section.The first section receives an oxygen-containing gas at a predeterminedflow rate and contains carbon-contaminated catalyst, wherein the firstsection is configured to provide a residence time of theoxygen-containing gas effective to selectively produce carbon monoxidefrom the carbon-contaminated catalyst, and the second section isconfigured to provide a second residence time of the oxygen-containinggas and carbon monoxide effective to produce carbon dioxide from thecarbon monoxide.

In a further contemplated aspect, the first section and the secondsection in preferred regenerators have a substantially circularhorizontal cross section, and it is especially preferred that the firstsection has a first height H₁ and a first diameter D₁, wherein thesecond section has a second height H₁ and a second diameter D₁, andwherein D₂:D₁ is at least 2.5 and H₂:H₁ is at least 0.6. Furthermore, itis contemplated that the first section is preferably operated at atemperature of less than 700° F., and the second section is preferablyoperated at a temperature of less than 1100° F.

In still further contemplated aspects, the carbon-contaminated catalystis fluidized in the first section at least in part at the predeterminedflow rate of the oxygen-containing gas, and the second residence time ofthe oxygen-containing gas and carbon monoxide in the second section issufficient to precipitate substantially all of the carbon-contaminatedcatalyst carried over from the first section. Moreover, the secondsection may receive a second oxygen-containing gas comprising molecularoxygen, especially in configurations where the oxygen-containing gas ofthe first section comprises an amount of molecular oxygen that issubstantially equal or less than an amount required to convertsubstantially all of the carbon of the carbon-contaminated catalyst tocarbon monoxide in the first section. Suitable regenerators may furtherinclude a catalyst coupled to the second section that converts residualcarbon monoxide to carbon dioxide.

Consequently, a method of regenerating a catalyst may include a step inwhich a regenerator vessel is provided having a first section fluidlycoupled to a second section, wherein the first section containscarbon-contaminated catalyst. In a further step, an oxygen-containinggas is fed to the first section at a predetermined flow rate, whereinthe first section is configured to provide a residence time of theoxygen-containing gas effective to selectively produce carbon monoxidefrom the carbon-contaminated catalyst, and wherein the second section isconfigured to provide a second residence time of the oxygen-containinggas and carbon monoxide effective to produce carbon dioxide from thecarbon monoxide.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a an exemplary configuration of a catalyst regeneratoraccording to the inventive subject matter.

DETAILED DESCRIPTION

The inventor has performed various calculations to more preciselyelucidate kinetics and equilibria for the two reactions governingoxidation of carbon to carbon dioxide via carbon monoxide, especially asit relates to regeneration of spent catalysts or solid particles in afluidized vessel.

Surprisingly, the data suggest for the limiting-step reaction (formationof carbon dioxide from carbon monoxide) that the conversion of carbonmonoxide to carbon dioxide is not equilibrium limited. Consequently,this conversion is thought to be kinetically limited, and will thereforebe significantly affected by pressure, temperature, residence time,oxygen intake, and effectiveness of mixing. Furthermore, calculationsfor the initial reaction (formation of carbon monoxide from carbon)indicated that the initial reaction is very rapid. Consequently, theinventor contemplates that the initial reaction may be conducted atrelatively low temperature, low oxygen intake, and short residence time.Viewed from another perspective, it should be appreciated that each ofthe two-step reactions has significantly different requirements inprocess kinetics. Moreover, additional calculations on the heat ofreaction suggested that the heat of reaction for the conversion ofcarbon monoxide to carbon dioxide is significantly higher than the heatof reaction for the conversion of carbon to carbon monoxide.

Therefore, the inventor contemplates that the conversion of carbon froma catalyst to carbon dioxide via the intermediate carbon monoxide can beperformed in a single vessel, wherein the first reaction from carbon tocarbon monoxide is selectively performed in a first section of thevessel at a first temperature, and wherein the second reaction fromcarbon monoxide to carbon dioxide is selectively performed in a secondsection of the vessel at a second temperature.

Consequently, in a particularly preferred aspect of the inventivesubject matter, a regenerator vessel may include a first sectioncontaining a carbon-contaminated catalyst and receiving anoxygen-containing gas at a flow rate, wherein the first section has afirst width and first volume. In contemplated vessels, a second sectionis fluidly coupled to the first section, wherein the second section hasa second width and second volume, wherein the first width and firstvolume and the second width and second volume are selected such that atthe flow rate (a) the oxygen-containing gas has a residence time in thefirst section effective to selectively produce carbon monoxide from thecarbon-contaminated catalyst, and (b) the oxygen-containing gas has aresidence time in the second section effective to produce carbon dioxidefrom the carbon monoxide.

As used herein, the term “residence time” of a gas in a vessel orsection of the vessel refers to the time which a predetermined volume ofthe gas requires to move through an imaginary horizontal plane throughthe vessel or section of the vessel. As also used herein, the term“selectively produce carbon monoxide from the carbon-contaminatedcatalyst” means that the ratio of carbon monoxide from thecarbon-contaminated catalyst to carbon dioxide (produced from carbonmonoxide) is at least 8:2, typically at least 9:1, more typically atleast 9.5:1, and most typically at least 9.8:1.

A particularly preferred exemplary configuration of a contemplatedregenerator 100 is depicted in FIG. 1, in which regenerator 100 has afirst section 110 (having height H₁ and diameter D₁) that is fluidlycoupled to a second section 120 (having height H₂ and diameter D₂).Oxygen-containing gas 130 enters the first section 110 and provides (atleast partial) fluidization of the carbon-contaminated catalyst beds 140in the first section 110. Where the regenerator 100 is continuouslyoperated, regenerated catalyst 140′ (not shown) is retrieved from thefirst section via opening 152, and carbon-contaminated catalyst 140 isprovided to the first section via opening 150. Second section 120receives (optional) secondary oxygen-containing gas 132, and the ventopening 160 of the second section 120 is coupled to a catalyst 162 thatconverts residual carbon monoxide to carbon dioxide in the vent gas 170.

It is generally contemplated that the first section and the secondsection in regenerators according to the inventive subject matter willhave a substantially circular (i.e., deviation in radius between tworadii no more than 15%) horizontal cross section. However, inalternative aspects, it should also be recognized that a particularshape of a section may be altered to adapt to a particular spatial orother requirement. For example, where suitable, the first or secondsection may have a square-shaped horizontal cross section. Regardless ofthe particular shape of the first and second sections, however, itshould be appreciated that first and second sections are configured suchthat the residence time of the oxygen-containing gas (which may or maynot include carbon monoxide and/or carbon dioxide) in the first sectionis less than the residence time of the oxygen-containing gas (which mayor may not include carbon monoxide and/or carbon dioxide) in the secondsection.

Consequently, and especially where the regeneration involves oxidationof carbon to carbon dioxide via carbon monoxide, it is preferred thatthe first section has a first height H₁ and a first diameter D₁, thesecond section has a second height H₂ and a second diameter D₂, and thatthe ratio of D₂:D₁ is at least 2.5 and the ratio of H₂:H₁ is at least0.6.

With respect to the first section, it is generally preferred that asubstantial portion (i.e., at least 60%, more typically at least 75%,and most typically at least 90%) of the carbon-contaminated catalyst isregenerated in the first section, preferably under conditions thatthermodynamically and/or kinetically favor formation of carbon monoxidefrom carbon, but not, or only to a minor extent, formation of carbondioxide from carbon (via carbon monoxide). Consequently, it is generallypreferred to operate the first section at a temperature of less than700° F.

Addition of spent catalyst (i.e., carbon-contaminated catalyst) to thefirst section is preferably performed through one or more ports proximalto the bottom portion of the first section. Depending on the type ofregeneration method, it is further contemplated that addition of thecatalyst may be continuous or batch-wise. Regenerated catalyst ispreferably removed from the first section, and the particular place ofremoval will at least in part depend on the shape and operation of thefirst section. However, it is generally preferred that the removal ofregenerated catalyst is proximal to either the bottom or the top of thefirst section. During operation, it is generally preferred that thecarbon-contaminated catalyst is fluidized in the first section. However,non-fluidized bed operational modes are also considered suitable andespecially include batch-mode operation (see below). Where the spentcatalyst is fluidized, it is especially preferred that fluidization isat least in part provided by the predetermined flow rate of theoxygen-containing gas.

It should be particularly appreciated that since the formation of carbonmonoxide from the carbon on the catalyst is fast and has lower kineticsrequirement than the requirements for subsequent conversion of carbonmonoxide to carbon dioxide, the first section is configured to promotethe first reaction (formation of carbon monoxide from the carbon) at alower temperature, a lower residence time, and lower oxygen intake.Thus, it is contemplated that preferred first sections will providesufficient contact between carbon-bearing catalyst and oxygen in theoxygen-containing gas to convert substantially all carbon topredominantly carbon monoxide. The relatively low temperature in thefirst section is particularly advantageous, since such operationaltemperatures allow use of less expensive metals and lower temperaturetolerant catalysts (and particularly those with lower sinteringtemperatures). Furthermore, it should be recognized that by virtue ofthe relatively low residence time requirement, the vessel diameter maybe significantly reduced. Moreover, it should be recognized that theheat of reaction from converting carbon to carbon monoxide and sulfur tosulfur dioxide (for a carbon and sulfur-bearing catalyst) willpredominantly provide the increase in process temperature.

Process condition in first section: It is generally contemplated thatthe first section of the regenerator unit will be designed under optimumprocess conditions (with properly selected temperature, residence timeand O₂ intake) to ensure that sufficient conversion of carbon from allspent catalysts to CO has occurred in first section. Optimum processconditions can be easily determined by monitoring the carbon content onthe regenerated catalysts leaving the regenerator (e.g., in grams ofcarbon per gram of catalyst).

For example, the process temperature in first section is generally setto the lowest point possible (based on the remaining carbon on thecatalyst) to reduce energy costs and damage to the catalyst whileensuring complete or sufficient (less than the maximum acceptableresidual carbon in the regenerated catalyst) conversion of C to CO infirst section. Calculations (see below) and commercially available datahave shown this required temperature to be far less than the 1200° F.operating temperature often used in a commercial unit, and can be as lowas 700° F., and even less.

As an example, the inventor contemplates N₂ as an inert fluidization gasand air as the oxygen source. A predetermined rate of air (typicallycontaining about 21% O₂) will be continuously injected into the N₂fluidization gas before the N₂ gas enters the regenerator. The N₂/airgas also serves as a heat sink to absorb the heat produced from theexothermic reaction (predominantly conversion of C to CO). The N₂/airmixture will be preheated before entering the regenerator unit whichprovides another means (control degree of preheat) to control thetemperature of the first section (e.g., to prevent run-off temperature).

The amount of required air injection rate to N₂ fluidization gas feed iscalculated based the need to sufficiently converting all C on catalyststo CO; to compensate for non-ideal mixing and inefficient contactbetween C on catalysts and O₂; and to satisfy the O₂ need for theinevitable amount of conversion of CO to CO₂. Note that the higher theN₂ intake rate (without exceeding the maximum fluidization gas rate),the lower the process temperature in first section.

Similarly, the oxygen demand in the first section may be determined bythe following considerations: (a) Conversion of all (or sufficient) C oncatalyst to CO, and further conversion of the produced CO to CO₂, and(b) additional oxygen and/or air to compensate for non-ideal mixing andinsufficient contact between O₂ and carbon on catalysts. Therefore, itshould be recognized that the first section in preferred configurationsprovides an O₂ deficient environment with respect to complete conversionof all C to CO₂, and an O₂ oversaturated environment with respect toconversion of all C to CO. Thus, and based on the rapid kinetics ofconversion of C to CO, a relatively low residence time in first sectionis required to promote the conversion of C to CO, which translates to arelatively small diameter of first section (as compared to the secondsection) and material savings.

With respect to the second section, it is generally contemplated thatthe shape and/or configuration is such that the velocity of theoxygen-containing gas comprising carbon monoxide in the second sectionis sufficiently low to precipitate substantially all (i.e., at least90%, more typically at least 95%, and most typically at least 99%) ofthe carbon-contaminated catalyst carried over from the first section.Moreover, it is generally contemplated that the second section isconfigured to provide a (second) residence time of the oxygen-containinggas and carbon monoxide coming from the first section effective to allowformation of carbon dioxide from the carbon monoxide produced in thefirst section.

It is generally preferred that the second section is continuous with thefirst section, wherein the transition from the first to the secondsection may include a tapered portion (as shown in FIG. 1), a rounded orotherwise shaped portion, or that the first section is directly coupledto a second section. A further particularly preferred additionalcomponent of the second section is a secondary oxygen-containing gasinlet that may provide an oxygen-containing gas that includes oxygen,preferably in an amount equivalent to an at least 1.1-fold molar excessover the carbon monoxide in the second section. It should further beespecially appreciated that the second section is preferably operated ata temperature of less than 1100° F., which is the generally acceptedmaximum allowable operating temperature for 316 stainless steel.

Thus, it should be particularly recognized that the first section isfluidly coupled to a “strategically expanded” second section of the sameregenerator vessel, wherein the majority of carbon monoxide is oxidizedto carbon dioxide at higher temperature, extended residence time, andrelatively high concentrations (e.g., 2-fold molar excess) of oxygen.Consequently, the high residence time translates in preferredconfigurations into a larger vessel diameter for the expanded section.Furthermore, the diameter and height of this expanded section of thevessel is strategically selected to provide sufficient residence time topromote the kinetically driven conversion of carbon monoxide to carbondioxide. It should be especially appreciated that the resultingappreciable amount of heat of reaction of the conversion of carbonmonoxide to carbon dioxide will provide the energy for the processtemperature in the upper expanded section.

Moreover, it is generally contemplated that catalyst entering the secondsection from the first section will already have a significantly reducedcarbon content (previously removed in the first section), and it isexpected that the residence time of the catalyst entering the secondsection will be sufficiently short (due to the lower flow rate in thesecond section) to avoid or reduce damage of the catalyst by the moresevere process conditions in the second section.

In an especially advantageous aspect of the inventive subject matter, itshould be recognized that the expansion in the second section will(besides increase in residence time and settling of catalyst) also serveas a surge vessel to dampen any cyclic or other peak production ofcarbon monoxide coming from the first section of the regenerator.

Furthermore it is contemplated that numerous gases are suitable asoxygen-containing gas for contemplated configurations and methods: andthe choice of a particular oxygen-containing gas will predominantlydepend on the particular type of reaction performed in the regenerator.In fact, it should be recognized that any gas comprising oxygen issuitable, so long as non-oxygen component(s) of the gas will not exhibitadverse effect on the catalysts (e.g., reduce capacity of the catalyst).However, it is generally preferred, and especially where the catalystcomprises a carbon-contaminated catalyst, that the regenerator gasincludes molecular oxygen.

Therefore, suitable regenerator gases include ambient air,oxygen-enriched or oxygen-depleted (ie., having an oxygen content ofless than 20 mol %) air, and numerous other natural and synthetic gases.Furthermore especially preferred oxygen-containing gases, and cparticularly those introduced into the first section of the regenerationvessel will comprise an amount of molecular oxygen that is substantiallyequal (i.e., ±5%) or less (e.g., between 5% and 25%, and even lower)than an amount required to convert substantially all of the carbon(i.e., at least 92%, more typically at least 95%) of thecarbon-contaminated catalyst to carbon monoxide in the first section.

Similarly, the nature of appropriate secondary oxygen-containing gases(i.e., oxygen-containing gas introduced into the second section) mayvary considerably, and the same considerations as described for theoxygen-containing gas above apply. However, in an especially preferredalternative aspect, the secondary oxygen-containing gas comprises oxygenin amount of at least 110%, more typically at least 130% of the amountrequired to convert substantially all of the carbon monoxide (ie., atleast 95%, more typically at least 98%) from the first section to carbondioxide in the second section.

It is generally contemplated that the second section is operated topredominantly service a gas phase reaction to convert CO to CO₂(however, some conversion of C to CO may still take place on the smallamount of catalysts entering the second section). Such CO conversion toCO₂ in the gas phase may be promoted by increase of residence time ofthe CO in the second section and/or increase of O₂ intake into thesecond section (via first section and/or separate oxygen intake). Sincethe CO to CO2 conversion is a highly exothermic process, it is generallycontemplated that the process temperature in the second section will bemonitored in order not to exceed the material temperature limit.

Calculation (see below) and commercial data have shown that the processtemperature in the second section can be maintained at or below 1100° F.and still promote sufficient conversion of CO to CO₂. In the event thatthe process temperature falls below a threshold for complete CO2formation, it is contemplated that a catalyst at exit of the secondsection will further promote the conversion of residual CO to CO2(wherein the exiting gas will have a sufficiently high temperature).Alternatively, or additionally, the second section of the regeneratorvessel wall may be reinforced with fire brick to accommodate occasionalor permanent temperatures of higher than 1100° F. Moreover, there arevarious alloy metals known in the art that resist temperatures higherthan 1100° F., and all of those may be employed fore use herein. Itshould be especially noted that temperatures exceeding 1100° F. aretolerable in the second section, since substantially no catalyst ispresent in the second section (or present long enough to be damaged).

O₂ control in the second section is relatively simple since the reactionin the second section is mostly a gas phase reaction (conversion in thesecond section of the CO₂ from the CO rising from the first section).Therefore, where appropriate, supplemental oxygen or oxygen-containinggas may be introduced into the second section and/or residence time ofthe CO may be increased.

Contemplated catalysts generally include all catalysts that can becontaminated during participation in a reaction, and especially thosewhere the contamination can be removed by oxidation with oxygen (O₂).Consequently, contemplated contaminations particularly include carbon(e.g., in the form of coke) and sulfur. Therefore, especiallycontemplated catalysts include those commonly employed in hydrotreating,hydrocracking, and FCC cracking. While not limiting to the inventivesubject matter, further particularly contemplated catalysts includethose that tend to sinter at or above a temperature of about 1100° F.

In still further contemplated regenerator configurations, and especiallywhere the increased residence time increased temperature from the onsetof the exothermic reaction of converting carbon monoxide to carbondioxide is not sufficient to meet the carbon monoxide emissionrequirements, additional components may be added to the regenerator. Forexample, in a particularly preferred option, a secondary oxygen/airintake stream may be provided to the second section or an additionalmixing device inside the section. Moreover, “in-situ” catalytic carbonmonoxide oxidization units may be coupled to the outlet of theregenerator.

Thus, and especially considering the foregoing, a particularly preferredregenerator will include a first section having a first height H₁ and afirst diameter D₁ and second section having a second-height H₁ and asecond diameter D₁, wherein D₂:D₁ is at least 2.5, H₂:H₁ is at least0.6, wherein carbon from a carbon-contaminated catalyst is selectivelyconverted to carbon monoxide in the first section, and wherein thecarbon monoxide from the first section is selectively converted tocarbon dioxide in the second section.

Consequently, a method of regenerating a catalyst will include one stepin which a regenerator vessel is provided having a first section fluidlycoupled to a second section, wherein the first section containscarbon-contaminated catalyst. In another step, an oxygen-containing gasis fed at a predetermined flow rate to the first section, wherein thefirst section is configured to provide a residence time of theoxygen-containing gas effective to selectively produce carbon monoxidefrom the carbon-contaminated catalyst, and wherein the second section isconfigured to provide a second residence time of the oxygen-containinggas and carbon monoxide effective to produce carbon dioxide from thecarbon monoxide. With respect to the first and second sections, thecarbon-contaminated catalyst, the oxygen-containing gas, the flow rate,and the residence time, the same considerations as described aboveapply.

It should be recognized that contemplated methods and configurations areparticularly useful in numerous applications, and an especiallypreferred use is in an FCC (Fluidized Catalytic Cracking) process forregeneration of spent catalysts, where known regenerators typicallyrequire high temperature resistant metals to complete oxidation in bothreactions in the same regenerator vessel. Other especially usefulapplications of contemplated regenerators include commercial catalystregeneration plants where oxidation of carbon is achieved in a singlefluidized bed vessel. Such known vessels typically produce 2000 ppmcarbon monoxide in the regenerator effluent stream, which is then burnedoff in a carbon monoxide boiler.

In yet another alternative aspect of the inventive subject matter, itshould be recognized that while a fluidized bed operation ofcontemplated regenerators is particularly preferred, batch mode, andespecially an alternating batch mode may be employed to regenerate thecatalyst. In such configurations, two devices according to the inventivesubject matter may be fluidly coupled such that a first device operatesas a regenerator, while a second device operates as catalytic reactoruntil the catalyst is sufficiently carbon-contaminated. Once the secondreactor contains enough carbon-contaminated catalyst and the firstreactor has regenerated the catalyst to a sufficient amount, theoperation is switched such that the first device operates as a catalyticreactor, and the second device operates as a regenerator.

Moreover, the inventive concept presented herein need not be limited toa particular application, so long as alternative applications require areaction vessel and proceed from an educt to a product via anintermediate through two kinetically different reactions. Thus, itshould generally be appreciated that a flow-through reactor for reactinga reagent via an intermediate to a product may comprise a first sectionfluidly coupled to a second section, wherein the first section receivesa reactant at a predetermined flow rate and contains the reagent,wherein the first section is configured to provide a residence time ofthe reactant effective to selectively produce the intermediate from thereagent, and wherein the second section is configured to provide asecond residence time of the reactant and the intermediate effective toproduce the product from the intermediate.

EXAMPLES Gas Phase Equilibrium Calculation

The formulae below were used for the calculations of equilibriumconstants for the conversion of CO to CO₂. As can be clearly seen, thecarbon to carbon monoxide reaction is very fast while the conversion ofcarbon monoxide to carbon dioxide is limiting and relatively slow. Theequilibrium constant for the limiting reaction at 1000° F. (538° K) iscalculated by using Gibbs energy, entropy and enthalpy to be 2.89×10²⁷,which is a relatively strong indicator that the carbon monoxide peakconcentration in known regenerator vessels of 1000 to 1500 ppm is notequilibrium limited. Consequently, under equilibrium condition, carbonmonoxide should be non-detectable. Viewed from another perspective,carbon monoxide peak production of 1500 ppm is severely limited bykinetics.2CO+O₂→2CO₂   (Equation 1) ΔG° _(f) (kJ/mol) −137.168 0 −394.359 ΔH°_(f) (kJ/mol) −110.525 0 −393.509 S° (J/Kmol) 197.674 205.138 213.74

Consequently,ΔG° _(r×n)=(2×−394.359)−(2×−137.168+0)=−514.382 kJ/mol,ΔH°_(r×n)=(2×−393.509)−(2×−110.525+0)=−565.968 kJ/mol.ΔS°_(r×n)=(2×213.74)−(2×197.674+205.138)=−173.006 J/K mol.

Based onΔG°=−RT ln K_(eq),ΔG°=ΔH−TΔS°, andΔH°−TΔS°=−RT ln K_(eq):ln K_(eq)=−ΔH°/RT+ΔS°/R and therefore R=8.314 J/K mol.

At a regenerator temperature of T=1000° F. (810° K.):ln K_(eq)=−ΔH°/RT+ΔS°/R,ln K_(eq)=−[−565.968 kJ/mol /(0.008314 kJ/K mol×810K)]+[−0.173006 kJ/Kmol/0.008314 kJ/K mol]:ln K_(eq)=63.233, which results in K_(eq)=2.89×10²⁷

When the reaction reaches equilibrium, K_(eq)=[CO₂]²/[CO]²[O₂]=2.89×10²⁷2CO+O₂→2CO₂100 ppm 4% 2-4%

At non-equilibrium conditions, Q=[CO₂]²/[CO]²[O₂]=[2]²/[0.1]²[4]=100Therefore Q<<K_(eq)

Gas Phase Rate Constant for CO Conversion

By assuming a second-order reaction, the calculations below presentcalculations of the kinetic rate constant for a gas phase reaction overa temperature range of 900 to 1500° F.(slow) CO+O₂→CO₂+O   Equation 2(fast) O+CO→CO₂   Equation 3(total) 2CO+O₂→2CO₂   Equation 1

The empirical correlation of rate constant, in the form of the Arrheniusequation, is obtained from the NIST database for the rate determiningslow step (Equation 2).

The calculation showed that the rate constant at 1500° F. is 1942 timesthe rate constant at 1000° F., the maximum operating temperature of theregenerator. This confirms the well known observation that carbonmonoxide can be easily destroyed at 1500° F. The calculation furthershowed that the rate constant at 1100° F. and 1200° F. are 6.8 and 35.6times respectively the rate constant at 1000° F. Although the inventorcontemplates that gas phase kinetics alone will only incompletelyrepresent the gas-solid interface reaction (with the presence of agas-solid interface, the activation energy is likely drasticallyreduced), it is contemplated that the 35.6 times improvement in gasphase kinetics, for instance, between 900 to 1200° F. may exhibitsufficient impact on the overall kinetics to lower carbon monoxide peakproduction to a level of less than 500 ppm.

Calculation: Gas phase kinetics rate constant calculations (using datafrom NIST and assuming a second order rate limiting reaction forequation 2)Rate=k[CO][O₂]k=Ae ^(−Ea/RT)=4.2×10⁻¹² e ^(−199547/8.314×T)=4.2×10⁻¹² e^(−199547/8.314×810)=5.67×10⁻²⁵

Therefore: T(° F.) T(K) 1000/T(K) k k/k @ 1000° F. 900 755 1.325 6.56 ×10⁻²⁶ 0.115 1000 810 1.234 5.67 × 10⁻²⁵ 1 1050 839 1.19 1.58 × 10⁻²⁴ 2.81100 866 1.155 3.86 × 10⁻²⁴ 6.8 1200 921 1.086 2.02 × 10⁻²³ 35.6 15001088 0.919 1.10 × 10⁻²¹ 1942

Under the assumption that the carbon monoxide content in the regeneratoreffluent is proportional (realizing that gas phase reaction alone likelywill not accurately represent the gas-solid interface reaction) to thesecond order rate constant with carbon monoxide content at 1000° F.being 1000 ppm, the following is the calculated carbon monoxide contentin a regenerator effluent. CO content in T [° F.] k/k at 1000° F.regenerator effluent 900 0.115 8695 ppm 1000 1 1000 ppm 1050 2.8 357 ppm1100 6.8 147 ppm 1200 35.6 28 ppm 1500 1942 0.5 ppm

Thus, it should be recognized that, based on the equilibrium K-value forthe conversion of carbon monoxide to carbon dioxide (K=2.89×10²⁷ at1000° F.), the conversion of carbon monoxide to carbon dioxide is notequilibrium limited. Furthermore, based on the calculated second orderreaction rate constant for conversion of carbon monoxide to carbondioxide at different temperatures (k=5.67×10²⁷ at 1000° F.), it shouldbe recognized that a temperature increase in the temperature range of900 to 1200° F. (which has generally been considered too low forcomplete combustion), will have a significant impact on the kinetics ofconverting carbon monoxide to carbon dioxide.

Still further, based on the second order reaction rate constant forconverting carbon on solid particles to carbon monoxide (k=1.6×10⁻¹¹ at68° F.) the inventor contemplates that the rate constant for convertingcarbon to carbon monoxide may be as high as 14 orders of magnitudehigher than the rate constant for converting carbon monoxide to carbondioxide, confirming the observation that conversion of carbon to carbonmonoxide is much faster than conversion of carbon monoxide to carbondioxide. Therefore, it should be recognized that the two reactions canbe segregated.

Moreover, it should be especially appreciated that, based on the heat ofreaction under ambient temperature (for the reaction C to CO, S to SO₂,and CO to CO2), the heat of reaction for converting carbon monoxide tocarbon dioxide (−566 kJ) is significantly higher than that of convertingcarbon to carbon monoxide (−221 kJ). For example, in the case of sulfurbearing catalyst, the heat of reaction for converting carbon monoxide tocarbon dioxide is roughly equal to the sum of heat of reaction forconverting carbon to carbon monoxide (−221 kJ) and S to SO₂ (−296 kJ).Consequently, it is contemplated that one can use the heat of reactionfor converting carbon monoxide to carbon dioxide as effective energysource for gas heating.

Based on the foregoing calculations and observations, the inventorcontemplates that every 1.7-time increase of the vessel diameter will beequivalent to a 50° F. increase in process temperature for kineticsenhancement, and that every 2.5-time increase of vessel diameter will beequivalent to 100° F. increase in process temperature for kineticsenhancement.

Thus, specific configurations and methods of improved catalystregenerators have been disclosed. It should be apparent, however, tothose skilled in the art that many more modifications besides thosealready described are possible without departing from the inventiveconcepts herein. The inventive subject matter, therefore, is not to berestricted except in the spirit of the-appended claims. Moreover, ininterpreting both the specification and the claims, all terms should beinterpreted in the broadest possible manner consistent with the context.In particular, the terms “comprises” and “comprising” should beinterpreted as referring to elements, components, or steps in anon-exclusive manner, indicating that the referenced elements,components, or steps may be present, or utilized, or combined with otherelements, components, or steps that are not expressly referenced.

1. A catalyst regenerator comprising: a first section containing acarbon-contaminated catalyst and receiving an oxygen-containing gas at aflow rate, wherein the first section has a first width and first volume;a second section fluidly coupled to the first section, wherein thesecond section has a second width and second volume; wherein the firstwidth and first volume and the second width and second volume areconfigured such that at the flow rate (a) the oxygen-containing gas hasa residence time in the first section effective to selectively producecarbon monoxide from the carbon-contaminated catalyst, (b) theoxygen-containing gas has a residence time in the second sectioneffective to produce carbon dioxide from the carbon monoxide to thereby(c) selectively limit oxidation of carbon to carbon monoxide in thefirst section and to allow oxidation of the carbon monoxide to carbondioxide in the second section; and wherein the flow rate in the firstsection is higher than the flow rate in the second section.
 2. Thecatalyst regenerator of claim 1 wherein the first section and the secondsection have a substantially circular horizontal cross section.
 3. Thecatalyst regenerator of claim 2 wherein the first section has a firstheight H₁ and a first diameter D₁, wherein the second section has asecond height H₂ and a second diameter D₂, and wherein D₂:D₁ is at least2.5 and H₂:H₁ is at least 0.6.
 4. The catalyst regenerator of claim 1wherein the carbon-contaminated catalyst has a temperature of less than700° F.
 5. The catalyst regenerator of claim 1 wherein the first sectionis configured such that the carbon-contaminated catalyst is fluidized inthe first section at least in part at the flow rate of theoxygen-containing gas.
 6. The catalyst regenerator of claim 1 whereinsecond section is configured such that the residence time of theoxygen-containing gas in the second section is sufficient to precipitatesubstantially all of the carbon-contaminated catalyst carried over fromthe first section.
 7. The catalyst regenerator of claim 1 wherein thesecond section receives a second oxygen-containing gas comprisingmolecular oxygen.
 8. The catalyst regenerator of claim 7 wherein theoxygen-containing gas received in the first section comprises an amountof molecular oxygen that is substantially equal or less than an amountrequired to convert substantially all of the carbon of thecarbon-contaminated catalyst to carbon monoxide in the first section. 9.The catalyst regenerator of claim 1 wherein the oxygen-containing gas inthe second section has a temperature of less than 1100° F.
 10. Thecatalyst regenerator of claim 1 wherein the carbon-contaminated catalystis continuously provided to the first section.
 11. The catalystregenerator of claim 1 further comprising a catalyst coupled to thesecond section that converts carbon monoxide to carbon dioxide.
 12. Acatalyst regenerator comprising: a first section having a first heightH1 and a first diameter D1 and second section having a second height H2and a second diameter D2, wherein D2:D1 is at least 2.5, H2:H1 is atleast 0.6; wherein carbon from a carbon-contaminated catalyst isselectively converted to carbon monoxide in the first section using anoxygen containing gas at a temperature of less than 700° F., and whereinthe carbon monoxide from the first section is selectively converted tocarbon dioxide in the second section at a temperature of less than 1100°F.; and wherein a flow rate of the oxygen containing gas is higher inthe first section than in the second section.
 13. A method ofregenerating a catalyst comprising: providing a regenerator vesselhaving a first section fluidly coupled to a second section, wherein thefirst section contains carbon-contaminated catalyst; feeding anoxygen-containing gas at a predetermined flow rate to the first section;wherein the first section is configured to provide a residence time ofthe oxygen-containing gas effective to selectively produce carbonmonoxide from the carbon-contaminated catalyst at a temperature of lessthan 700° F.; wherein the second section is configured to provide asecond residence time of the oxygen-containing gas and carbon monoxideeffective to produce carbon dioxide from the carbon monoxide at atemperature of less than 1100° F.; and wherein the flow rate in thefirst section is higher than in the second section.
 14. The method ofclaim 13 wherein the first section has a first height H₁ and a firstdiameter D₁, wherein the second section has a second height H₂ and asecond diameter D₂, and wherein D₂:D₁ is at least 2.5 and H₂:H₁ is atleast 0.6.
 15. The method of claim 13 further comprising operating thefirst section at a temperature of less than 650° F. and operating thesecond section at a temperature of less than 1050° F.
 16. The method ofclaim 13 wherein the second residence time of the oxygen-containing gasand carbon monoxide in the second section is sufficient to precipitatesubstantially all of the carbon-contaminated catalyst carried over fromthe first section.
 17. The method of claim 13 further comprising feedinga second oxygen-containing gas comprising molecular oxygen to the secondsection.
 18. The method of claim 13 wherein the oxygen-containing gas ofthe first section comprises an amount of molecular oxygen that issubstantially equal or less than an amount required to convertsubstantially all of the carbon of the carbon-contaminated catalyst tocarbon monoxide in the first section.
 19. The method of claim 13 furthercomprising continuously providing the first section withcarbon-contaminated catalyst.
 20. The method of claim 13 furthercomprising coupling a catalyst to the second section that convertsresidual carbon monoxide to carbon dioxide.